1. Field of the Invention
The present invention relates to an abnormality detection alarm circuit for an output circuit, by which an abnormal condition use to an open or short status of a load driven by an output circuit can be detected to deactivate the output circuit for protection, while generating an alarm signal.
2. Description of the Prior Art
Various output circuits with high current drive faculty are connected to an output stage of electronic circuits in order to drive a load coupled to the output stage thereof.
In these output circuits, in case the load is shorted, since an overcurrent higher than the allowable current will be passed through an output transistor constituting an output stage of the circuit, the output transistor will be broken down due to this overcurrent. To protect the output transistor when the load is shorted, a protection circuit is usually incorporated in the output circuit to protect the output transistor from the overcurrent passed through the shorted output transistor.
In these prior-art protection circuits, however, only when the load is shorted, the output transistor is protected from the overcurrent. Therefore, no countermeasure has been taken against such a malfunction that the load is open or approximately in open status (e.g. a load connecting wire is about to be disconnected). In other words, it has been impossible to easily and quickly detect an abnormality or a malfunction of an output circuit (e.g. short or open status of the load) serving as a part of an entire system (e.g. electronic apparatus) and further to restore the abnormal circuit to the normal conditions as quickly as possible.